This invention relates to the reception, handling and evaluation of empty beverage containers. Systems for performing such functions have particular applicability to a supermarket environment, where large numbers of returnable beverage containers must be redeemed for their deposit values. Prior art systems of this general type are disclosed in Planke U.S. Pat. No. 3,955,179, Planke U.S. Pat. No. 4,055,834, and in Dubberly et al U.S. patent application Ser. No. 924,855.
As disclosed in Planke U.S. Pat. No. 3,955,179, a container is recognized by transporting it through an illumination station, where it is illuminated by a large beam of light. A shadow of the container is projected against a screen and is detected by a series of photodetectors which are strategically mounted within the screen. Output signals from the photodetectors are applied to evaluation circuitry, which recognizes the container and generates a signal representing the deposit value thereof. The system totals the deposit values for a series of containers which are so recognized and prints a redemption ticket indicating the computed total value.
Planke U.S. Pat. No. 4,055,834 discloses a container recognition system wherein the container is transported through the path of a vertically sweeping laser beam. A bundle of optical fibers is arranged to receive signals from the sweeping laser along a series of vertically arranged points. The fibers are arranged to carry light from their receiving ends to the face of a photodetecting device. The photodetecting device then generates an electrical signal which represents the contour of the container. Means are provided for processing this signal to recognize the container and print a redemption ticket.
Dubberly et al teaches a container recognition system wherein the container is placed upon a conveyor equipped with an encoder device. The movement of the conveyor causes the encoder to generate a series of conveyor clock pulses representing actual physical movement of the container. The container is transported through an illumination station where it blocks the light falling upon a series of vertically arranged photodetectors. When the leading edge of the container first blocks any photodetector, that photodetector generates a light-to-dark transition signal, which causes a series of associated counters to begin counting conveyor clock pulses. These counters count to predetermined minimum counts at which time they open registration "windows" by enabling associated registration circuits. The counters then continue counting to predetermined maximum counts, during which counting the registration circuits are operative to produce container recognition signals.
According to the Dubberly et al teaching, the photodetectors remain operative throughout the time period of the registration window and continually look for the trailing edge of the container. When the trailing edge of the container comes into view the photodetectors sense a dark-to-light transition. This dark-to-light transition causes generation of trailing edge signals. The trailing edge signals are applied to those registration devices which are associated with the signal generating photodetectors. If a registration device receives such a trailing edge signal while it is enabled, then a container recognition signal is generated. When the counters reach their predetermined maximum counts, they close their registration windows by disabling their associated registration circuits.
It has been observed that when some types of glass bottles are being illuminated as taught in Dubberly et al, the background is completely darkened. During the time that the photodetectors are being blocked from the illumination source they sometimes see bright spots due to reflection of light within the structure of such glass bottles. In fact, some bottles may create bright spots which are even brighter than the unblocked illumination source itself.
When the photodetectors see a bright spot within a container, they are likely to interpret the spot as the trailing edge of the container. Such an interpretation causes application of a trailing edge signal to all registration circuits which are connected to the spot-observing photodetector. Any such registration circuits which are enabled at that time will generate an erroneous recognition signal.